1. Field of the Invention
The present invention relates to spinal disc prostheses used to replace human spinal discs damaged by trauma or disease.
2. Description of the Related Art
As humans age, the water content of the nuclei in their spinal discs decreases. At the same time, the collagen content of the nuclei increases; such disc degradation results in a more rigid nucleus that is more like the surrounding annulus. These changes in the disc can make the annulus more prone to traumatic injuries, such as circumferential tears. Multiple tears in an annulus can create a xe2x80x9cgapxe2x80x9d through which the nucleus can escape. This is event is commonly referred to as a herniated disc, which causes pain as the displaced nucleus presses against adjacent nerves.
Disc degradation also disrupts the loading patterns within the spine. Moreover, experts have observed a direct correlation between disc degradation and the formation of laterally growing osteophytes which can result in pressure being applied to adjacent neural tissue. Generally, disc degradation ultimately results in pain. Most frequently, the degradation occurs in the lumbar region (lower back) of patients and results in sciatica, a pain that begins in the lower back an travels down the sciatic nerve in the leg.
There are two standard surgical procedures used to treat problems associated with intervertebral (or spinal) disc degradation; these are discectomy and arthrodesis. Discectomy is the removal of part or all of a spinal disc. The procedure involves the removal of disc material that may be impinging on surrounding nerves, thereby relieving any associated lower back or leg pain. However, discectomies can sometimes result in redistributed spinal loading stresses, post operative spinal instability, or other problems. Some statistics report that although 48% to 86% of discectomies are initially successful, i.e. the patient experiences no more pain after surgery, the pain often returns over time. Ten years after surgery 60% to 70% of patients experience back pain again, and 25% to 30% have recurrent sciatica.
Arthrodesis (or spinal fusion) is another common surgical treatment for spinal disc degradation problems. Spinal fusion is used to prevent the spine from moving in a specific area of the spine and is often performed in conjunction with a discectomy. The procedure increases the stability of a patient""s spine around affected vertebrae of a damaged or removed disc, and prevents further degradation of the treated area.
Between 50% and 94% of patients have good to excellent results immediately after arthrodesis1. However, years after surgery problems can arise including spinal stenosis, vertebral osteophyte formation, and disc degeneration adjacent to the treated location. These problems generally result in a return of pain.
A need exists, therefore, for a method for and means of treating spinal disc degradation and related problems that reduces or eliminates the long term problems associated with presently employed treatments, such as discectomy or arthrodesis. Those of skill in the art have realized that a solution to the problems described above requires a prosthetic spinal disc. A viable prosthetic disc may result in a variety of additional benefits including shorter patient recovery time, a decrease in number of people who experience chronic back pain, and a decrease in revision spinal fusions. Generally, those of skill in the art employ one of three prosthetic disc design concepts, all of which have disadvantages that ultimately limit there success. These concepts include nucleus replacement, mechanical discs, and composite discs.
Nucleus replacement involves removal and replacement of a damages nucleus. This approach assumes that the annulus and end-plates are uncompromised. Consequently, nucleus replacement is useful only during the early stages of disc degeneration where minimal segment collapse has occurred. Also, nucleus replacement requires placing a hole in the annulus to insert the prosthetic nucleus. Because the prosthetic nucleus is thereafter unsecured, it is sometimes ejected from the disc through the hole.
Mechanical discs and composite discs, the second and third disc replacement concepts, generally comprise a polymer center bounded by metallic end-plates having growth promoting surfaces for long term fixation to surrounding bone and prongs or spikes to accommodate short term fixation to the same. These discs require a relatively invasive surgical procedure in which a large incision is made directly anterior to the affected area, and a path is generated between the anterior incision and desired surgical location. Furthermore, mechanical and composite discs generally comprise parallel end-plates, which do not correspond to natural end-plates which normally have non-parallel adjacent vertebrae. This inconsistency between prosthetic discs known to those of skill in the art and natural discs may result in loading and deformation problems for a patient""s spine.
Thus, a need exists for an artificial spinal disc and method of using the same for treating disc degradation and related problems that restores or maintains the spinal function at all stages of disc degeneration.
A further need exists for an artificial spinal disc and method of using the same for treating disc degradation and related problems, wherein the disc includes a prosthetic analog for each component of a natural disc.
A further need exists for an artificial spinal disc and method of using the same for treating disc degradation and related problems that can be employed in a manner that is minimally invasive to the patient.
A still further need exists for an artificial spinal disc and method of using the same for treating disc degradation and related problems that employs a more anatomically correct prosthetic disc.
The present invention, in one form thereof, is a prosthetic artificial disc comprising an annulus, a nucleus, and a pair of endplates. The prosthetic disc of the present invention is expandable such that it may be inserted into a patient""s body in a minimally invasive manner.
The present invention, in broad terms, comprises an expandable, generally ring shaped annulus having, when expanded, the shape, functional properties and mechanical properties of a natural spinal disc annulus. The annulus surrounds a prosthetic spinal disc nucleus. The nucleus of the present invention comprises an expandable shell, having, when expanded, the shape, functional properties and mechanical properties of a natural spinal disc nucleus. Finally, the invention comprises a pair of flexible spinal disc endplates that are attached superiorly and inferiorly to the prosthetic annulus, thereby containing the prosthetic nucleus within the annulus. The endplates provide stability to the prosthetic disc and a means of fixation to vertebra that are adjacent to the treated area.
The present invention further comprises a method of inserting a prosthetic spinal disc in a human body using relatively less invasive techniques than prior art surgical methods.
An advantage of the present invention is that the disc of the present invention is useful in treating disc degradation and related problems, and it restores or maintains spinal function at all stages of disc degeneration.
Another advantage of the present invention is that the disc of the present invention includes a prosthetic analog for each component of a natural disc.
Yet another advantage of the present invention is that it can be used in treating disc degradation and related problems in a manner that is minimally invasive to the patient.
A still further advantage of the present invention is that it employs a more anatomically correct prosthetic disc.